From your comment/question - I take it you are running desktop Linux
A. - Were things working correctly? (I guess so - you said it)
1st - if you had LAMMP set up to -autostart- in some fashion - make sure it is running
'/opt/lampp/lampp status' will do the trick
What happens when you go to "http://localhost/xampp" ?
Did you install any new software?
Did you 'update software' via a desktop script/application ?
Did you update your Firefox browser? try to Install Chrome, or Opera and see if the problem persists
Try accessing your site from another machine, it does not have to be Linux -
B. - The reason for my suggestions -
LAMPP probably did not decide to become 'HAL 9000', and the message wasn't "I'm sorry PhdJ, I can't do that" - its unlikely your httpd.conf needs tinkering because there is no likely reason it should have changed (so I agree with your basic premise).